SkQP: error image now opaque

Also more explanation in the report.

Change-Id: I1d91efb5b5af064d90da5383e4182c8cef197e0c
Reviewed-on: https://skia-review.googlesource.com/101541
Reviewed-by: Hal Canary <halcanary@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
1 file changed